(1) Field of the Invention
The present invention relates generally to sonar systems, and more particularly to a method of operating a continuous wave (CW) sonar system using multiple, unique-frequency pulses.
(2) Description of the Prior Art
In the field of continuous wave active sonar, it is known that performance can be enhanced by lengthening the transmission pulse. This results in narrow transmission bandwidths since bandwidth is equal to 1/T (units of hertz or Hz) where T is the length in time of the transmission pulse in seconds. Such narrower transmission provides fine frequency resolution at the receiver portion of the sonar system thereby providing good noise discrimination. However, in the medium frequency range of 1.5 to 5 kHz, usually target dynamics and the environment spread the bandwidth of an echo return to 1 Hz or more no matter how narrow the transmission pulse. Thus, while long transmission pulses offer greater transmission sharpness, most of this transmission energy is wasted as echo returns spread to at least 1 Hz.